How do I add a rainbow fire effect?

So, I have been working on effects for people to get however, I have one more that I cannot figure out how to do. A rainbow fire effect. It basically is a color changing flame. This is the flame script I use:

return function(Knife)
    local Fire = Instance.new("Fire", Knife.Handle)
    Fire.Heat = 5
    Fire.Size = 2
end

Here is the blue version:

return function(Knife)
	local Fire = Instance.new("Fire", Knife.Handle)
	Fire.Heat = 5
	Fire.Size = 3
	Fire.Color = Color3.fromRGB(0, 85, 255)
end

Now I am looking for a rainbow color changing fire, anyone offering for help? Or just give me the whole script? It would be very much appreciated.

There are many things wrong with your code.

First of all, please add a code block. (Thanks, youtubemasterWOW)

Before you start a function you set it up like:

function NAME(parameters)
end

And when you give a function parameter(s), you must call the function and give the parameters. Example:

function NAME(parameters)
parameter:Destroy()
end

local part = script.Parent

NAME(part)

Here's the code:

function Knife(Knife)
    local Fire = Instance.new("Fire", Knife.Handle)
    Fire.Heat = 5
    Fire.Size = 2
end

function Knife2(Knife)
    local Fire = Instance.new("Fire", Knife.Handle)
    Fire.Heat = 5
    Fire.Size = 3
    Fire.Color = Color3.fromRGB(0, 85, 255)
end

local Knife1 -- what knife1 is
local Knife2 -- what knife2 is

Knife(Knife1)
Knife2(Knife2)